On the assumption that a router is separated into Control Element (CE, control section) and Forwarding Element (FE, data transfer section), an approach for defining a control protocol between CE and FE has been made in a Forwarding and Control Element Separation (ForCES) Working Group (WG) for Internet Engineering Task Force (IETF).
Also, an IP packet communication system in which the device is separated into a control section and a data transfer section, like the separated model between CE and FE, is disclosed (e.g., refer to patent document 1).
Though the control section is often called a C-plane and the data transfer section is called a U-plane or D-plane, a method for controlling the connectivity between the C-plane controller and the U-plane controller is disclosed (e.g., refer to patent document 2).
The C-plane, which means Control Plane, designates a link through which data of control message exchanged between the devices is passed. Also, the U-plane, which means User data Plane, designates a link through which various contents data actually transmitted and received between the user terminals are passed.
A router or switch making up the conventional network system including the internet adopts a device configuration in which a C-plane control function and a U-plane control function are unified. In the conventional network system, when the message traffic of the C-plane increases, and when the message traffic of the U-plane increases, expansion is required in units of router or switch.
On the contrary, in an architecture in which the C-plane control function and the U-plane control function are distinct, as described above, one of the aims is to improve the cost effectiveness in the respect of scalability wherein when the message traffic of the C-plane increases, the C-plane controller is expanded, while when the message traffic of the U-plane increases, the U-plane controller is expanded.
A rapid expansion of the internet has one aspect that the characteristic of the node devices such as routers exchanging the routing information with each other using a routing protocol has contributed to autonomous and dispersive extension of the network. On the other hand, however, from the viewpoint of network management, there is a problem that it is difficult to grasp and control the communication route which dynamically varies autonomously.
To cope with this problem, in a network architecture having C/U separation in which the C-plane controller and the U-plane controller are separated, it is intended to grasp the communication route more easily by integrating information of the C-plane and enable an active routing control.
Also, the U-plane controller performs the data transfer, based on the routing information set from the C-plane controller, and continues the data transfer in accordance with the already set routing information, as long as there is no explicit change of the routing information. By operating in this way, it is intended that faults in the C-plane do not affect the operation of the U-plane.    Patent document 1: Japanese Patent No. 3256494    Patent document 2: JP-A-2005-278178